One of the steps in production of glass optical fibers is a so called collapse phase. During this phase, a deposited glass tube is contracted in a contraction machine to a glass rod (also known as an optical fiber preform), utilizing a heat source. The contraction machine is generally known as a collapser. The machine has a heat source at a temperature higher than a melting temperature of the deposited glass tubes (above 2000 degrees Celsius). Suitable heat sources for collapsing the glass tubes include hydrogen/oxygen burners, plasma burners, electrical resistance furnaces, and induction furnaces.
Unfortunately, the tube can break during the collapsing process. The broken glass can severely damage the heat source. This will often lead to costly reparation of the heat source as well as the adjustment of the collapse recipe. This causes further process stability problems.
The problem is especially urgent for tubes having deposited layers with relatively high germanium content (e.g., providing a refractive index difference between the substrate tube and the deposited layers higher than 0.5%).